This invention relates to methods and apparatus for shaping metal cylinders and the like, and more particularly relates to improved methods and apparatus for reforming crushed drill pipe.
It is well known that oil and gas is found in subsurface earth formations, and that these petroleum substances are usually recovered through boreholes drilled into the formation from the surface. It is also well known that most such boreholes are drilled with rotary-type drilling equipment, wherein a "string" of drill pipe having a drill bit suspended at its lower end is revolved in the borehole to cut away the rock and other earth materials beneath the bit.
What is not well known outside of the drilling industry itself is that rotation of the drill string in the borehole tends to erode or abrade away the outside surface of the drill pipe, and this in turn tends to gradually reduce the tensile strength of the various lengths or sections of pipe composing the drill string. This, in turn, affects the overall integrity of the drill string, since the integrity of the drill string will obviously depend upon the strength of each section of pipe in the string.
It will be readily apparent that if the drill string breaks at any time during the drilling of the well, this will create a serious situation for both the well owner and the drilling contractor. It is extremely costly to drill a conventional oil or gas well, even without the additional expense of a special crew and equipment to fish out a section of the drill string from the borehole. Further, it is extremely expensive for the regular drilling crew to stand idly by with its equipment, while the fishing crew attempts to remove the lost section of drill string. Accordingly, the petroleum industry has necessarily adopted standards for evaluating the quality of drill pipe, and has further adopted a clearly recognized set of limits to determine the conditions under which so-called "used" or partly worn drill pipe may be employed to drill an oil or gas well.
The top grade of used drill pipe, which is commonly referred to as "premium", is drill pipe having at least 80% of its original wall thickness, and therefore such pipe will have a value approaching that of unused or new pipe, since it may be used to drill all but the very deepest of boreholes. "Class 2" drill pipe is that which has at least 65% of its wall thickness remaining, and "Class 3" drill pipe is that which has at least 55% of its original wall thickness remaining. "Class 4" drill pipe, which is ordinarily available only for drilling shallow water wells and the like, is pipe having less than 55% of its original wall thickness remaining.
It should be noted, however, that these standards only apply to drill pipe (other than Class 4 pipe) having no other flaws or defects such as cracks, dents or compressional deformities or the like. Thus, if a length of drill pipe has a dent or other flaw, it will usually be assigned to Class 3 or 4 regardless of its wall thickness, and will therefore have a market or sales value which is one-third or less than the usual value of pipe having such a wall thickness.
A length of drill pipe may, of course, become damaged or flawed for any number of different reasons. A particularly common occurrence is, however, for the pipe to be crushed under pressure of the slips in the rotary drilling table, where the drill string is being supported by these slips while sections of pipe are being unscrewed from or screwed onto the drill string. This may occur because the crewman is inadvertently applying too great a gripping pressure to the drill pipe, but it more often occurs because the slips or cones become worn to the extent that they tilt so as to apply pressure against too small a portion of the outside surface of the drill pipe.
It should be appreciated that, while this overcompression or crushing of the sections of drill pipe will occur at the same location (immediately below the box) along each section of pipe, the extent of such crushing will be relatively small and will usually not be visible to all but the most trained and experienced eye. Consequently, it will often occur that each section of an entire drill string of 15,000 feet or more will be crushed and thereby rendered unsuitable, before the problem is discovered. Moreover, this can occur regardless of the initial grade or class of the drill pipe, and thus the entire length of a drill string worth over $300,000.00 (at $21.00 per foot) may, in a few minutes, be inadvertently reduced to its scrap value. Further, there is the additional expense of having the drilling rig and crew stand down while an attempt is made to acquire a new drill string which may, or may not be, immediately available.
There have been many attempts to meet this problem, and in particular there have been attempts made to develop apparatus to reform crushed drill pipe by internally squeezing it outwardly to its original shape. For example, there may be seen the devices which are disclosed, for example, in U.S. Pat. Nos. 1,153,663 and 2,461,565, which provide for applying pressure to swell the pipe. Even though the extent of the crush usually experienced is relatively minor, as hereinbefore stated however, such attempts have not been acceptable to the industry for several reasons.
First, it should be noted that the reforming operation must be performed without heating or otherwise distorting the drill pipe so as to further affect its tensile strength. Accordingly, this requires that the reforming step be performed as sharply and abruptly as the original crushing step was performed.
Second, and perhaps because of this first aspect of the problem, it should be noted that the reforming step must be performed so that the pipe is swelled to only its original shape, since an outwardly bulged length of drill pipe will be rejected for the same reason that the crushed section was rejected. Even the slightest degree of overreforming is unacceptable, and since the reforming step must be performed within the section of pipe where it cannot be observed, it will readily be apparent that this is no simple task.
Third, any apparatus for reforming crushed drill pipe must, to be acceptable, be capable of handling a large number of sections of drill pipe within a relatively small time interval, and with a minimum amount of expertise on the part of its operator. None of the techniques and devices which have heretofore been proposed, however, have met these requirements to an extent acceptable to the industry.
Another reason why the prior art devices have been unsuitable for reforming drill pipe involves the peculiar special shape of a length of drill pipe as such. More particularly, it should be noted that not only does drill pipe commonly have a relatively thick or heavy wall in contrast to well casing and the like, it also has an even smaller diameter throat section adjacent the "box" or internally threaded portion at its upper end. Thus, a section of drill pipe is provided with an abnormally heavy wall section which creates a restriction in the form of an annular shoulder within the interior of the drill pipe. Further, this internal restriction or narrowing is located below the box but above the section of pipe which usually experiences crushing.
It will thus be apparent that, if a device is inserted into the end of the pipe to apply an expanding pressure at the zone of the crush, the device must not only be collapsible to an extent that it is insertable into the crushed section, but it must be further collapsible to an extent that it pass through this particularly narrow section below the box but above the crushed section of the pipe. This, of course, is in addition to the other requirements of the device, as hereinbefore set forth, and thus it will readily be apparent why devices such as those depicted or suggested in U.S. Pat. Nos. 1,153,663 and 2,461,565 have not been accepted by the industry for the purposes recited.
These disadvantages of the prior art are overcome with the present invention, however, and improved methods and apparatus are herewith provided for restoring crushed drill pipe sections and the like to their original configuration and condition.